The present invention is directed to a gas cluster ion beam apparatus. More particularly, the present invention is directed to a gas cluster ion beam apparatus that enables effective separation of monomer or molecular ions from the gas cluster ion beam.
Moreover, the present invention is directed to a gas cluster ion beam apparatus capable of controlling multiple independent adjustments through an automated electronic control system.
Energetic-ion sputtering has been conventionally used for etching and thinning in manufacturing and depth-profiling in analytic instruments. However, energetic-ion sputtering causes subsurface damage and accumulated roughness because energetic-ion sputtering uses monomer ions. Individual monomer atoms or molecules have energies on the order of thousands of electron volts that cause the residual surface damage.
To avoid the residual surface damage, gas cluster ion beam process devices have been developed. One example of such an apparatus, as well as the creation and acceleration of such a conventional gas cluster ion beam, is described in U.S. Pat. No. 5,814,194to Deguchi et al. The entire contents of U.S. Pat. No. 5,814,194 are hereby incorporated by reference. Another example of a gas cluster ion beam apparatus is described in U.S. Pat. No. 5,459,326 to Yamada. The entire contents of U.S. Pat. No. 5,459,326 are hereby incorporated by reference.
Gas cluster ion beams can be used for etching, cleaning, and smoothing of material surfaces in certain applications. These conventional gas cluster ion beams comprise gas clusters having nano-sized aggregates of materials that are gaseous under conditions of standard temperature and pressure. Such clusters are typically formed of aggregates of approximately 20 to approximately several thousand atoms or molecules loosely bound together. The gas clusters can be ionized by electron bombardment or other means, permitting the gas clusters to be formed into directed beams of known and controllable energy. The larger sized gas clusters are the most useful because the larger sized gas clusters are able to carry substantial energy per cluster ion, while yet having only modest energy per atom or molecule.
The gas clusters disintegrate on impact with each individual atom or molecule carrying only a small fraction of the total cluster energy. Consequently, the impact effects of large clusters, while substantial, are limited to only a very shallow surface region, thereby enabling ion clusters to be effective for a variety of surface modification processes, without the tendency to produce deeper subsurface damage. As noted above, deeper subsurface damage is a characteristic of monomer or molecular ion beam processing.
One characteristic of gas cluster ion interactions with surfaces is ultra-shallow interaction depth. The gas cluster ion interactions also exhibit inherent smoothing and planarization behaviors. These behaviors can be extraordinary when the gas cluster ion impacts upon rough or non-planar surfaces. Since the atoms within a cluster are able to interact with each other as the cluster disintegrates upon impact, some of the energy carried by the cluster is converted into energy of individual atoms within the cluster. This converted energy is dissipated in all directions within the plane of the target surface, thereby producing excellent smoothing behavior on most materials, including diamond. Lastly, the gas cluster ion interactions demonstrate an ability to produce enhanced surface chemical reactions with reactive cluster species.
Gas cluster ions deposit their total energy into the impact site upon the target surface. The atoms within a gas cluster ion have small individual energies that prevent the atoms from penetrating beyond very shallow depths of a few atomic layers. Consequently, a gas cluster ion deposits considerable energy into a much shallower region on the target surface than would a monomer or molecular ion of equal energy. Similarly, since the gas cluster ion has much greater mass and momentum, a gas cluster ion impact can generate much more intense pressure pulse effects than those associated with monomer ion bombardment.
Computer simulations of gas cluster ion impacts predict peak momentary temperatures of the order of 100,000xc2x0K in combination with pressure pulses in the range of millions of pounds per square inch. These transient high temperature and pressure conditions within the impact volume occur while the gas atoms from the cluster are being dynamically mixed with the target material atoms, thereby enabling highly enhanced chemical reaction properties to be observed or realized.
Conventionally, gas cluster ion sources produce gas clusters ions having a wide distribution of sizes, N (where N=the number atoms or molecules in each cluster). Such atoms in a cluster are not individually energetic enough (on the order of a few electron volts) to significantly penetrate a surface to cause the residual surface damage typically associated with the other types of ion beam processing, such as energetic-ion sputtering.
However, the gas cluster ion can be made sufficiently energetic (some thousands of electron volts), to effectively etch, smooth or clean surfaces. This allows the gas cluster ion to be used to smooth surfaces of various materials to nearly an atomic scale by utilizing all-dry vacuum methods. Such materials include, but are not limited to, silicon, compound semiconductors, dielectric wafers, films and high-dielectrics, thin metal and ferromagnetic films, and electro-optics.
An example of a prior art gas cluster ion beam apparatus 100 is illustrated in FIG. 1. As illustrated in FIG. 1, the gas cluster ion beam apparatus 100 includes a vacuum vessel 102 that is divided into three communicating chambers, a source chamber 104, a ionization/acceleration chamber 106, and a processing chamber 108. The three chambers are evacuated to suitable operating pressures by vacuum pumping systems 146a, 146b, and 146c, respectively. A condensable source gas 112 (for example argon, Ar) is admitted under pressure through gas feed tube 114 to stagnation chamber 116 and is ejected into the substantially lower pressure vacuum through a properly shaped nozzle 110.
The gas feed tube 114, the stagnation chamber 116, and the nozzle 110 together constitute the gas feed assembly, thereby producing a supersonic gas jet 118. Cooling, resulting from the expansion in the jet, causes a portion of the gas jet 118 to condense into clusters, each cluster consisting of from several to several thousand weakly bound atoms or molecules.
In FIG. 1, a gas skimmer 120, having an aperture, separates the gas products that have not been formed into a cluster jet from the cluster jet. This separation minimizes the pressure in the downstream regions where higher pressures would be detrimental (e.g., ionizer 122, high voltage electrodes 126, and process chamber 108). Suitable condensable source gases 112 include, but are not necessarily limited to, argon; nitrogen and other inert gases; oxygen; carbon dioxide; oxides of nitrogen; and sulfur hexafluoride.
After the supersonic gas jet 118 containing gas clusters has been formed, the clusters are ionized in ionizer 122. The ionizer 122 is typically an electron impact ionizer that produces thermoelectrons from one or more incandescent filaments 124. The ionizer 122 accelerates and directs the electrons causing the electrons to collide with the gas clusters in the gas jet 118, at the point where the jet passes through the ionizer 122. The impact of the electrons causes electrons from the clusters to be ejected, thereby causing a portion of the clusters to become positively ionized. The positive ionization is usually, but not necessarily, with a single charge.
A set of suitably biased high voltage electrodes 126 extracts the cluster ions from the ionizer, forming a beam. The biased high voltage electrodes 126 then accelerates the cluster ions to a desired energy (typically adjustable from 1 keV to several tens of keV) and focuses the cluster ions to form a gas cluster ion beam 128.
Filament power supply 136 provides voltage VF to heat the ionizer filament 124. Anode power supply 134 provides voltage VA to accelerate thermoelectrons emitted from filament 124 to cause the thermoelectrons to bombard the cluster containing gas jet 118 to produce ions. Extraction power supply 138 provides voltage VE to bias a high voltage electrode to extract ions from the ionizing region of the ionizer 122 and to form the gas cluster ion beam 128. Accelerator power supply 140 provides voltage VAcc to bias a high voltage electrode with respect to the ionizer 122 so as to result in a total gas cluster ion beam acceleration energy equal to VAcc. One or more lens power supplies, 142 and 144, bias high voltage electrodes with potentials, VL1 and L2, to focus the gas cluster ion beam 128.
A workpiece 152, which may be a semiconductor wafer or other workpiece to be processed by gas cluster ion beam 128, is held on a workpiece holder 150, disposed in the path of the gas cluster ion beam 128. Since most applications contemplate the processing of large workpieces with spatially uniform results, a scanning system is desirable to uniformly scan the gas cluster ion beam 128 across large areas to produce spatially homogeneous results.
Two pairs of orthogonally oriented electrostatic scan plates 130 and 132 are utilized to produce a raster or other scanning pattern across the desired processing area. When beam scanning is performed, the gas cluster ion beam 128 is converted into a conical scanned gas cluster ion beam 148, which scans the entire surface of workpiece 152.
The core of this technology is predicated on the efficient generation, ionization, and controlled transport of a gas cluster ion beam 128 made up of clusters of gaseous ions to the surface of a workpiece 152 to be modified. A stream of pure gas, for example argon, is introduced into a vacuum environment through a modified Laval nozzle 118. The modified Laval nozzle 118 has a very small throat aperture and expands causing the gas to form large molecular clusters which exit the horn of the nozzle 118 in a concentrated core stream surrounded by a more diffuse cloud of monomer atoms or molecules.
The gas jet 118 has a central core of gas clusters, which is the useful portion of the gas stream and must be separated from the balance of the non-clustered gas atoms or molecules. This is done by directing the gas jet 118 through the small aperture of a gas skimmer 120 that passes the core cluster beam into a high vacuum ionization/acceleration chamber 106. The small aperture of a gas skimmer 120 skims the non-clustered gas molecules to be pumped away. This beam of gas clusters is then passed through an array of high voltage electrodes 126, exiting as a fully formed gas cluster ion beam 128, to be used in the aforementioned processing applications.
Considering the variety of potential production applications in the semiconductor and in other industries, there is great need for a gas cluster ion beam processing equipment that is compatible with the low maintenance, high production requirements of such industries. There have been several problems with conventional gas cluster ion beam equipment, which has primarily been designed for and used in laboratory or research environments. These problems have heretofore hindered the successful application of gas cluster ion beam processing in high volume industries.
One example of a problem with the conventional gas cluster ion beam equipment is that the conventional gas cluster ion beam equipment lacks a simple, inexpensive, and reliable means for separating monomer (or in the case of molecular gases, molecular) ions from the gas cluster ion beam. As noted above the inclusion of the monomer ions in the gas cluster ion beam can cause unwanted surface damage to the substrate being processed.
Moreover, the conventional gas cluster ion beam apparatus lacks efficient and automatic means for sequentially handling workpieces to move the workpieces into and out of the vacuum processing environment. This is important in a production environment as opposed to a research or laboratory environment. If the workpiece cannot be handled efficiently, the productivity of the gas cluster ion beam apparatus is negatively impacted.
Lastly, conventional gas cluster ion beam apparatus have no effective and fast means for aligning the neutral cluster jet produced by the nozzle with the aperture of the gas skimmer. Aligning the nozzle/gas skimmer assembly so that the beam exiting the nozzle is centered on the skimmer aperture and normal to and centered in the discs of the high voltage electrodes assembly is critical. Also since the ion beam is somewhat divergent as it leaves the nozzle, it is essential to have the correct spacing between the nozzle exit and the gas skimmer entrance. If this spacing is too large many of the clusters at the outer perimeter of the beam will be clipped away by the skimmer causing a loss of cluster beam throughput and an overall loss of performance.
Thus, it is an object of the present invention to provide an automated electronic control system capable of controlling the multiple independent adjustments of the gas cluster ion beam apparatus under programmable control to permit quick and efficient setup of a pre-selected beam condition and to maintain that condition during processing and to manage the sequential processing of multiple workpieces.
Another object of the present invention is to provide a simple, effective, reliable and inexpensive means for removing monomer or molecular ions from the gas cluster ion beam.
It is a further object of the present invention to provide automatically controllable endstation means for transferring workpieces to be processed into and out of the processing chamber for rapid, efficient production flow of workpieces through the gas cluster ion beam processor.
It is a still further object of the present invention to provide improved means for adjustable alignment of nozzle and gas skimmer to optimize gas cluster ion beam production. It is an objective that the alignment is accurate and repeatable and that the adjustments are fast and simple.
The present invention provides a solution to the problems set forth above with respect to the conventional gas cluster ion beam apparatus.
One aspect of the present invention is a substrate surface treatment method. The method forms gas cluster particles comprising a plurality of atoms or molecules; accelerates the gas cluster particles; filters accelerated gas cluster particles using a permanent magnet beam filter; and irradiates the accelerated magnetically selected gas cluster particles onto a surface of a substrate in a reduced pressure atmosphere.
A second aspect of the present invention is a substrate surface treatment apparatus. The apparatus includes an ionizer to form gas cluster particles comprising a plurality of atoms or molecules; a power supply to accelerate the gas cluster particles; a permanent magnet beam filter to select certain accelerated gas cluster particles; and scan plates to irradiate the magnetically filtered accelerated gas cluster particles onto a surface of a substrate in a reduced pressure atmosphere.
A third aspect of the present invention is a substrate surface treatment method. The method forms gas cluster particles comprising a plurality of atoms or molecules; accelerates the gas cluster particles; focuses the accelerated gas cluster particles using a lens combination to realize a long focal length; and irradiates the accelerated magnetically selected gas cluster particles onto a surface of a substrate in a reduced pressure atmosphere.
A fourth aspect of the present invention is a substrate surface treatment apparatus. The apparatus includes an ionizer to form gas cluster particles comprising a plurality of atoms or molecules; a power supply to accelerate the gas cluster particles; a lens combination to focus the accelerated gas cluster particles to realize a long focal length; and scan plates to irradiate the magnetically filtered accelerated gas cluster particles onto a surface of a substrate in a reduced pressure atmosphere.
A fifth aspect of the present invention is an apparatus for smoothing a surface of a substrate. The apparatus includes an ionizer to form gas cluster particles comprising a plurality of atoms or molecules; a power supply to accelerate the gas cluster particles; a lens assembly to focus the accelerated gas cluster particles; a filter to filter the focussed gas cluster particles; scan plates to irradiate the filtered accelerated gas cluster particles onto a surface of a workpiece situated in a reduced pressure atmosphere chamber; and a substrate loading/unloading mechanism to load and unload the workpiece. The substrate loading/unloading mechanism provides a workpiece from a plurality of workpieces onto a holder positioned at a first position within the reduced pressure atmosphere chamber, the first position being substantially parallel to a central axis of a flow of the filtered accelerated gas cluster particles. The substrate loading/unloading mechanism also moves the holder with a workpiece thereon to a second position, the second position being substantially perpendicular to the first position and the central axis of a flow of the filtered accelerated gas cluster particles.
A sixth aspect of the present invention is an apparatus for smoothing a surface of a substrate. The apparatus includes an ionizer to form gas cluster particles comprising a plurality of atoms or molecules; a power supply to accelerate the gas cluster particles; a lens assembly to focus the accelerated gas cluster particles; a filter to filter the focussed gas cluster particles; scan plates to irradiate the filtered accelerated gas cluster particles onto a surface of a workpiece situated in a reduced pressure atmosphere chamber; and a substrate loading/unloading mechanism to load and unload the workpiece. The ionizer includes an alignment device wherein the alignment device includes a X/Y translation element having micrometer driving heads with opposing return spring assemblies and an angular translation element having micrometer driving heads with opposing return spring assemblies.
A seventh aspect of the present invention is an apparatus for smoothing a surface of a substrate. The apparatus includes an ionizer to form gas cluster particles comprising a plurality of atoms or molecules; a power supply to accelerate the gas cluster particles; a triode/Einzel lens combination assembly to focus the accelerated gas cluster particles; a permanent magnet beam filter to filter the focussed gas cluster particles; scan plates to irradiate the filtered accelerated gas cluster particles onto a surface of a workpiece situated in a reduced pressure atmosphere chamber; and a substrate loading/unloading mechanism to load and unload the workpiece. The ionizer includes an alignment device wherein the alignment device includes a X/Y translation element having micrometer driving heads with opposing return spring assemblies and an angular translation element having micrometer driving heads with opposing return spring assemblies. The substrate loading/unloading mechanism provides a workpiece from a plurality of workpieces onto a holder positioned at a first position within the reduced pressure atmosphere chamber, the first position being substantially parallel to a central axis of a flow of the filtered accelerated gas cluster particles. The substrate loading/unloading mechanism also moves the holder with a workpiece thereon to a second position, the second position being substantially perpendicular to the first position and the central axis of a flow of the filtered accelerated gas cluster particles.